1. Field of the Invention
The present invention relates to a method for evaluating a liquid repellent film on parts which are subjected to a liquid repellent treatment. The present invention particularly relates to a method for evaluating the quality of a liquid repellent film wherein by containing a substance absorbing or emitting electromagnetic waves, the transmittance or reflectance ratio of electromagnetic waves, or fluorescence intensity is measured in a repellent film, and the characteristics of the liquid repellent film are evaluated from a map of the relationship between the film thickness and the contact angle with a liquid, which has been determined in advance.
2. Description of the Prior Art
A fuel injection valve (referred to as an injector hereinafter) of an internal combustion engine, etc. must surely stop a fuel flow or allow a suitable amount of the fuel to flow by opening or closing the valve. Moreover, foreign materials such as oil, additives and moisture are present in the fuel, and accumulations, which are so-called deposits and which hinder the flow of the fuel, etc., form while the engine is running. When deposits are accumulated, they hinder the fuel flow, and cause a failure of the internal combustion engine even if the injector constituent parts are prepared with high precision. Various parts have recently been improved by being subjected to a repellent film treatment for the purpose of decreasing the adhesion of such deposits. However, such a film is colorless and transparent in the visible light region, and very thin. As a result, discrimination of the film itself is difficult. When the film is not formed in a predetermined manner, the desired effects cannot be exhibited. Judgement of the formation of the liquid repellent film and evaluation of the film, therefore, becomes important.
The thickness of a film used for electronic and mechanical parts has heretofore been from around 100 nm to 0.1 mm. Observation of a cross section with an electron microscope, a fluorescent X-ray thickness meter, or the like used in the measurements cannot be used for measuring the thickness of a liquid repellent film having a thickness of up to 100 nm. In order to improve such measurement methods, the following methods have been proposed: a method for estimating the liquid repellency of a liquid repellent film from its optical properties; a method for estimating the liquid repellency from the physical properties of a liquid used in the inspection; and a method for estimating the liquid repellency wherein a liquid is used in the inspection, the liquid repellency and a capillary phenomenon act on the liquid, and the liquid repellency is estimated from the physical properties.
Although all the methods mentioned above are nondestructive ones, costly apparatuses such as an infrared spectrometer, a refractometer and a polarized light analyzer become necessary for measuring the optical properties. Moreover, attention and labor are required for handling and controlling the liquid in the method of using a liquid, and there is much restriction on the physical properties (including the shape, etc.) of the material to be measured.
On the other hand, Japanese Unexamined Patent Publication (Kokai) No. 4-338137 discloses a water repellent film obtained by substituting a fluoroalkyl group for part of a ceramic integrally formed on a glass substrate as a water repellent glass and mainly containing SiO.sub.2.
Such a water repellent film is favorable to adhesion and hardness, and the treated film can be evaluated by the method as mentioned above. However, there still remain the same problems. Accordingly, development of an evaluation method is desired, which achieves the evaluation of such water repellent films, which solves the problems as mentioned above and which is simple and favorable in cost.